1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device using a semiconductor thin film, and more particularly to a method of manufacturing a thin film transistor (TFT) using a crystalline silicon film.
In the present specification, the semiconductor device is directed to all of devices that function using semiconductor, and includes not only a single device such as a TFT but also an electro-optic device, an electronic device on which the electro-optic device is mounted, etc.
2. Description of the Related Art
In recent years, thin film transistors used in an electro-optic device such as an active matrix liquid crystal display device have been actively developed.
The active matrix liquid crystal display device is directed to a monolithic display device having a pixel matrix circuit and a driver circuit on the same substrate. Also, a system on-panel in which a logic circuit such as a memory circuit or a clock generating circuit is built has been progressively developed.
Since the driver circuit and the logic circuit of the above type require high-speed operation, it is improper to use an amorphous silicon film as an active layer. For that reason, in the existing circumstances, a TFT using a crystalline silicon film (polysilicon film) as an active layer is being mainly used.
The present inventors disclose a technique in Japanese Patent Unexamined Publication No. Hei 8-78329 as a technique for obtaining a crystalline silicon film on a glass substrate. The technique disclosed in that publication is that catalytic elements that promote crystallization are selectively added to an amorphous silicon film, and a heat treatment is then conducted on the film to form a crystalline silicon film that spreads frown a catalytic element added region as a starting point.
This technique makes it possible to lower the crystallization temperature of the amorphous silicon film down to 50 to 100xc2x0 C. due to the action of the catalytic elements, and also makes it possible to reduce a period of time required for crystallization down to ⅕ to {fraction (1/10)}. Further, because the crystallization of a silicon film progresses laterally substantially in parallel with a substrate surface, the present inventors call this crystallization region xe2x80x9clateral growth regionxe2x80x9d.
Since the catalytic elements are not directly added to the lateral growth region, the catalytic elements remaining in the film is less than that in the case where the catalytic elements are directly added. For example, in the case of directly adding the catalytic elements, the catalytic elements are contained in the film in the orders of 1019, but in case of the lateral growth region, the orders in which the catalytic elements are contained are 1018 which is reduced one digit.
The above crystallizing technique enables a silicon film having excellent crystallinity to be obtained at a relatively low temperature. However, since the catalytic elements are contained in the film, to control the amount of introducing the catalytic elements is delicate, thereby leading to a problem on reproducibility and stability (stability of the electric characteristics of an obtained device).
Also, an influence of the catalytic elements remaining in the film cause such problems that the characteristics of the obtained semiconductor device are varied as a time elapses, that an off-state value which is a characteristic value of the thin-film transistor is large.
As the catalytic elements used for promoting the crystallization, there are used metal elements such as nickel or cobalt, and if the catalytic elements are even slightly contained in the film, they adversely affect the electric characteristic and the reliability of the TFT.
Accordingly, it is ideally desirable that the catalytic elements are perfectly removed from the film after a crystallizing process.
Under the above circumstances, in order to reduce the concentration of catalytic elements existing in the crystallized crystalline silicon film, elements selected from Group XV (15) are selectively added to the crystalline silicon film, and a heat treatment is conducted on that film-under an oxygen atmosphere, to thereby make the concentration of catalytic elements reduce. However, the catalytic elements cannot be completely removed from the interior or the surface of the film by only the above process, and also in a process of conducting a heat treatment on the crystalline silicon film in an oxygen atmosphere, the catalytic elements existing in the film react with oxygen to form an oxide, and there appears a phenomenon that the oxide abnormally grows on the surface and in the interior of the film.
The oxide that has abnormally grown has a size of several xcexcm, and in the case of using a mask made of the oxide, because the oxide is removed together with the mask in a mask removing process for forming a semiconductor island region, holes are produced in the surface and interior of the film, thereby leading to the failure of the characteristic of the thin film transistor.
As described above, the oxide that abnormally grows causes a problem in forming a semiconductor island region.
The present invention has been made to solve the above problem, and therefore an object of the present invention is to provide a technique for preventing an oxide that abnormally grows from generating.
Another object of the present invention is to provide a technique for preventing the oxide that abnormally grows from generating, and removing catalytic elements existing in a crystallized crystalline silicon film to reduce the concentration of catalytic elements to a degree that the characteristic of a transistor is not affected by that concentration.
To achieve the above objects, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
selectively forming an insulating film on an amorphous silicon film;
selectively adding catalytic elements that promote the crystallization of silicon to the amorphous film with the insulating film as a mask;
transforming at least a part of the amorphous silicon film into a crystalline silicon film through a heat treatment;
selectively adding elements selected from Group XV to the crystalline silicon film with the insulating film as a mask;
gettering the catalytic elements to a region in which the elements selected from Group XV are added from a region adjacent to the region through a heat treatment; and
removing only the region to which the elements selected from Group XV are added.
Also, according to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
selectively forming an insulating film on an amorphous silicon film;
selectively adding catalytic elements that promote the crystallization of silicon to the amorphous film with the insulating film as a mask;
transforming at least a part of the amorphous silicon film into a crystalline silicon film through a heat treatment;
selectively adding elements selected from Group XV to the crystalline silicon film with the insulating film as a mask;
gettering the catalytic elements to a region in which the elements selected from Group XV are added from a region adjacent to the region through a heat treatment; and
removing only the region to which the elements selected from Group XV are added, and removing or reducing the catalytic elements existing in the crystalline silicon film and the elements selected from Group XV from a section where the region is removed, through a heat treatment in an atmosphere containing halogen elements therein.
Further, according to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
selectively forming an insulating film on an amorphous silicon film;
selectively adding catalytic elements that promote the crystallization of silicon to the amorphous film with the insulating film as a mask;
transforming at least a part of the amorphous silicon film into a crystalline silicon film through a heat treatment;
selectively adding elements selected from Group XV to the crystalline silicon film with the insulating film as a mask;
gettering the catalytic elements to a region in which the elements selected from Group XV are added from a region adjacent to the region through a heat treatment;
removing a region to which the elements selected from Group XV are added; and
removing or reducing the catalytic elements existing in the crystalline silicon film and the elements selected from Group XV, through a heat treatment in an oxidizing atmosphere containing halogen elements therein.
Furthermore, according to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor device comprising the steps of:
selectively forming an insulating film on an amorphous silicon film;
selectively adding catalytic elements that promote the crystallization of silicon to the amorphous film with the insulating film as a mask;
transforming at least a part of the amorphous silicon film into a crystalline silicon film through a heat treatment;
selectively adding elements selected from Group XV to the crystalline silicon film with the insulating film as a mask;
gettering the catalytic elements to a region in which the elements selected from Group XV are added from a region adjacent to the region through a heat treatment;
removing a region to which the elements selected from Group XV are added;
patterning the crystalline silicon film to form an island region;
covering the island region with an insulating film; and
conducting a heat treatment in an oxidizing atmosphere containing halogen elements therein.
It is desirable that the region to which the catalytic elements are added and the region to which the elements selected from Group XV are added are formed by the same insulating film mask.
A basic object of the present invention is to remove the catalytic elements used for crystallization of the amorphous film containing silicon from the crystalline film, and as means for achieving this object, there is used the gettering effect of the elements selected from Group XV.
The catalytic elements are representatively Ni (nickel), Co (cobalt), Fe (iron), Pd (palladium), Pt (platinum), Cu (copper), and Au (gold). According to the experiments of the present inventors, it is found that nickel is the most proper element.
The elements of Group XV which getters the catalytic elements are N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony) and Bi (bismuth), and in particular, what exhibits remarkable action and effect is P (phosphorus).
The addition of the elements of Group XV may be made through the ion plantation method or the plasma doping method.
Those methods are different from each other in that the former method is to mass-separate only the element ions of a single substance to add them whereas the latter is to add also the composite ions containing elements without conducting mass-separation. For example, in the case where the plasma doping method is used for addition of P, since PH3 (phosphine) is employed as a plasma doping gas, compound such as PH2 or PH3 are contained in the film in addition to P. However, elements that impedes the gettering effect are not contained in the film. The same is applied to other elements.
As a representative example, in the case where nickel and phosphorus are used as catalytic elements and gettering elements (elements of Group XV), respectively, phosphorus and nickel exhibit a stable bond state through a heat treatment at about 600xc2x0 C. In this situation, there are bond states of Ni3P, Ni5P2, Ni2P, Ni3P2, Ni2P3, NiP2 and NiP3.
As described above, in the case where nickel is used as catalytic elements that promote the crystallization of an amorphous film containing silicon, nickel can be gettered by the action of phosphorus which is an element of Group XV. The use of this effect makes it possible to remove or reduce catalytic elements from the interior of the crystalline silicon film.
However, this gettering process is insufficient to remove nickel, and nickel slightly remains in the crystallize silicon film.
When remaining nickel is exposed to and reacts with oxidizing gas, nickel suicide is oxidized to produce an oxide that grows in the form of a band on the surface of the film and in the interior thereof.
In particular, nickel reacts with oxygen so that NiOx abnormally grows on the surface of the film and in the interior thereof.
In order to prevent the above oxide (NiOx) from abnormally growing, in addition of gettering due to the heat treatment, the nickel added region is etched by a gas in which halogen elements are added to an inactive gas atmosphere after the crystallizing process, so as to selectively remove a film containing a large amount of Ni and P.
It is preferable that the atmosphere containing halogen S elements contains one or plural kinds of gases selected from HCl, HF, HBr, Cl2, F2 and Br2.
In this way, nickel elements are removed to prevent the formation of the oxide which causes a problem.
Also, it is desirable that the semiconductor device is produced such chat the oxidizing gas is out of contact with the crystalline silicon film as much as possible through all the processes after the crystallizing process.
In addition, the most characteristic structures of the present invention are listed below.
(1) An insulating film (mask) is selectively provided on the amorphous film, and catalytic elements are added to the film, to thereby form a crystalline film called xe2x80x9clateral growth regionxe2x80x9d.
(2) The above mask is used as it is, and elements having a gettering effect are added to the film, to thereby getter the catalytic elements that remain in the lateral growth region.
(3) The above mask is used as it is, and the nickel added region or the phosphorus added region is removed.
That is, the technique disclosed in Japanese Patent Unexamined Publication No. Hei 8-78329 is utilized in crystallization of the amorphous film, and the insulating film remaining on the crystalline film which has been crystallized is reused as a mask for selectively adding the elements of Group XV. The disclosure of 8-78329 patent is incoporated herein by reference.
Also, the mask is reused when removing the region (nickel added region) containing nickel and phosphorus with high concentration.
Accordingly, the region to which the catalytic elements are added and the region to which elements selected from Group XV are added are made to be the same region.
Also, since the mask insulating film used when adding nickel is reused when adding P ions, there is no necessity of newly providing a mask used in the P-ion adding process. Further, since the mask insulating film used when adding nickel is reused when removing the region (nickel added region) containing nickel and phosphorus with high concentration, there is also no necessity of newly providing a mask used in the nickel added region removing process.
Accordingly, the manufacturing process is simplified, a manufacture yield and through-put are improved, thereby obtaining an economically superior effect.